Do not use this, as PDO has been moved into core (the php source) so this pecl extension is dead.

PDO provides a uniform data access interface, sporting advanced features such
as prepared statements and bound parameters. PDO drivers are dynamically
loadable and may be developed independently from the core, but still accessed
using the same API.

Release notesVersion 0.2.4(beta)

Note that PDO on its own is useless.
You need to install a PDO database driver to make use of it,
check http://pecl.php.net for a list of available PDO drivers.

It is highly recommended that you update to the latest stable PHP 5 snapshot
before using PDO.
You can obtain it from http://snaps.php.net.

If you are running on Windows, you should download:
http://snaps.php.net/win32/php5.0-win32-latest.zip
http://snaps.php.net/win32/PECL_5_0/php_pdo.dll